In U.S. Pat. No. 4,627,654, Van Oost discloses a gripper adapted for gripping circular work pieces or work pieces having a circular bore comprising a support plate, a plurality of articulated parallelograms which are disposed in planes converging toward a common axis, each of the parallelograms including a first arm parallel to the common axis which is movable by means of an axial piston in a direction parallel to the axis and another arm provided with rollers disposed on each side of the support which is extendible or retractable in response to movement of the first arm. This latter extensible arm is also provided with fingers for clamping the workpiece when the extensible arm is either extended or retracted.
In U.S. Pat. No. 4,566,845 to Al Mouhamed et al., a gripper device is disclosed having a pair of fingers which can be displaced to grasp an article to be handled, each finger being formed by a support and a contact plate which contacts the article. The gripper module is provided with several degrees of freedom including rotational movement about a spindle axis, translation of the contact plate and rotation of the contact plate about its axis. Compressible displacement measuring pickups deliver information associated with their deformation related to the force on an object about these three degrees of motion.
The above mentioned patents are examples of useful grippers module having degrees of freedom which provide flexibility for robots. The needs of each robot must be considered individually.
A cylindrical robot is typically provided with a vertical shaft on a support base which supports a horizontal arm. Various end-effectors or hands may be attached to the end of the robot arm. The robot arm may move either up or down on the vertical shaft, may rotate about the vertical shaft or may extend or retract in order to access various locations on a table or other work space. In order to allow the hand of the robot to grasp objects in the workspace, it is necessary for the robot to be able to orient its gripping elements with respect to the object. Whereas anthropomorphic robots having joints structured like human shoulders, elbows and wrists have sufficient degrees of freedom to orient the hand in a direction suitable to grab objects, cylindrical robots are not usually provided with these degrees of freedom. Even anthropomorphic robots may need an extra degree of freedom for greater flexibility or precision.
A problem with many prior art grippers is that their utility is limited because they are driven from the robot arm. This requires that the gripper have connectors which mate with a specific robot arm for both electrical and mechanical functions. In other words, the gripper-robot interface is cumbersome.
It is an object of the present invention to provide a robot hand or gripper having supplemental degrees of freedom to those already found on robots with a simple gripper-robot interface so as to enable the gripper to grasp objects of any orientation on a work space, with fine precision, regardless of the type of robot arm to which it is attached.